Adaptable overlays for forward error correction schemes based on trellis codes

Abstract

A method and apparatus for providing auxiliary data in a idle potion of a slot in a time division multiple access system is disclosed. A speech coder converts speech into digital signals that are coupled to a convolutional coder. The convolutional coder processes the digital signals using three or four connection polynomials to create two sets of outputs. One set of outputs, which is generated from first and second connection polynomials is identical to the standard output of a IS-136 convolutional coder. The second set of outputs, which are the auxiliary data, are generated using third and fourth connection polynomials. The second set of outputs is coupled to a puncturing function, which appropriately deletes portions of the second set of outputs. The remaining portion of the second set of outputs is transmitted in the idle portion of a time slot.

What is claimed is:  
     
       1. A method of generating and transmitting auxiliary digital information in a communication system, comprising the steps of: 
       identifying digital data for transmission;  
       applying a plurality of connection polynomials to the digital data to generate a standard set of convolutionally coded data and an auxiliary set of convolutionally coded data;  
       puncturing the standard set of convolutionally coded data to create a standard set of punctured data;  
       puncturing the auxiliary set of convolutionally coded data to create an auxiliary set of punctured data;  
       broadcasting the standard set of punctured data in a first transmission slot; and  
       broadcasting the auxiliary set of punctured data in a second transmission slot, wherein the second transmission slot is in known relationship with the first transmission slot in time.  
     
     
       2. The method of claim  1 , wherein the step of puncturing the auxiliary set of convolutionally coded data comprises determining an amount of information that can be transmitted in the second transmission slot. 
     
     
       3. The method of claim  1 , wherein the second transmission slot comprises a variable size. 
     
     
       4. The method of claim  1 , wherein the second transmission slot and the first transmission slot are of identical size. 
     
     
       5. The method of claim  1 , wherein the second transmission slot can accommodate approximately 100 bits. 
     
     
       6. The method of claim  1 , wherein the method is used in conjunction with a cellular communication system. 
     
     
       7. The method of claim  1 , wherein the digital data for transmission includes an input bit stream that produces common input bits at known positions in the standard set of convolutionally coded data and in the auxiliary set of convolutionally coded data. 
     
     
       8. The method of claim  7 , wherein the number of common input bits is at least equal to a maximum memory of a function performing the convolutional encoding. 
     
     
       9. The method of claim  7 , wherein the common input bits comprise class Ia+CRC bits. 
     
     
       10. The method of claim  7 , wherein the common input bits comprise class Ib bits. 
     
     
       11. An apparatus for generating and transmitting auxiliary coded digital information in a communication system, comprising: 
       a digital signal source for providing digital signals;  
       a convolutional coder connected to the digital signal source, wherein the convolutional coder processes the digital signals to produce a standard set of coded signals and an auxiliary set of coded signals, wherein the standard set of coded signals is created from a first connection polynomial and a second connection polynomial and the auxiliary set of coded signals is created from a third connection polynomial and a fourth connection polynomial;  
       a transmission control function connected to the convolutional coder for determining whether to transmit the auxiliary set of coded signals; and  
       a puncturing function in communication with the convolutional coder, wherein the auxiliary set of coded signals are coupled to the puncturing function.  
     
     
       12. The apparatus of claim  11 , wherein the puncturing function deletes portions of the auxiliary set of coded signals. 
     
     
       13. The apparatus of claim  11 , wherein the digital signals generated by the digital signal source comprise class I bits and class II bits. 
     
     
       14. The apparatus of claim  13 , wherein the auxiliary set of coded signals is used to protect the class II bits. 
     
     
       15. The apparatus of claim  11 , wherein the apparatus is used in conjunction with a cellular communication system. 
     
     
       16. The apparatus of claim  15 , wherein the operation of the cellular communication system is based on an IS-136 standard. 
     
     
       17. A method of decoding digitally-encoded data that are received on a plurality of time slots, comprising the steps of: 
       collecting data from the plurality of time slots;  
       calculating path metrics relevant to a first class of data in a first section of a decoder trellis;  
       splitting the first section of the decoder trellis into a second section of a decoder trellis and a third section of a decoder trellis;  
       updating the second section of the decoder trellis with the path metrics;  
       updating the third section of the decoder trellis with the path metrics;  
       identifying a first maximum likelihood path corresponding to the second section of the decoder trellis and a second maximum likelihood path corresponding to the third section of the decoder trellis, both the first maximum likelihood path and the second likelihood path traversing the first section of the decoder trellis;  
       identifying a set of decoded data bits from the first maximum likelihood path and the second maximum likelihood path, wherein the bits associated with the first maximum likelihood path pertain to a first class of data and the bits associated with the second maximum likelihood path pertain to a second class of data and the bits pertaining to a third class of data are associated with one of the first maximum likelihood path and the second maximum likelihood path.  
     
     
       18. The method of claim  17 , wherein the path metrics are Viterbi decoder path metrics. 
     
     
       19. The method of claim  17 , wherein the first class of data comprises a portion of moderately significant data. 
     
     
       20. The method of claim  17 , wherein the second class of data comprises a portion of least significant data. 
     
     
       21. The method of claim  17 , wherein the third class of data comprises a portion of the most significant data. 
     
     
       22. The method of claim  17 , further comprising the steps of: 
       merging the second section of the decoder trellis and the third section of the decoder trellis into a common fourth section of a decoder trellis;  
       updating the fourth section of the decoder trellis with path metrics obtained from the second section of the decoder trellis and the third section of the decoder trellis, wherein the updates to the fourth section of the decoder trellis pertains to a fourth class of data;  
       identifying continuations of the first maximum likelihood path and the second maximum likelihood path through the fourth section of the decoder trellis; and  
       identifying decoded data bits for the fourth class of data from one of the first maximum likelihood path and the second maximum likelihood path.  
     
     
       23. An apparatus for generating and transmitting auxiliary coded digital information in a communication system, comprising: 
       a digital signal source for providing digital signals;  
       a convolutional coder connected to the digital signal source, wherein the convolutional coder processes the digital signals to produce a standard set of coded signals and an auxiliary set of coded signals, wherein the standard set of coded signals is created from a first connection polynomial and a second connection polynomial and the auxiliary set of coded signals is created from a third connection polynomial and a fourth connection polynomial;  
       a transmitter, adapted to broadcast the standard set of coded signals in a first transmission slot and the auxiliary set of coded signals in a second transmission slot; and  
       a transmission control function, coupled to the convolutional coder and adapted to determine whether to transmit the auxiliary set of coded signals.  
     
     
       24. The apparatus of claim  23 , wherein the digital signals generated by the digital signal source comprise class I bits and class II bits. 
     
     
       25. The apparatus of claim  24 , wherein the auxiliary set of coded signals are adapted to protect the class II bits from encoding. 
     
     
       26. The apparatus of claim  23 , further comprising a puncturing function in communication with the convolutional coder, wherein the auxiliary set of coded signals are coupled to the puncturing function. 
     
     
       27. The apparatus of claim  26 , wherein the puncturing function deletes portions of the auxiliary set of coded signals. 
     
     
       28. The apparatus of claim  23 , wherein the apparatus is used in conjunction with a cellular communication system. 
     
     
       29. The apparatus of claim  28 , wherein the operation of the cellular communication system is based on an IS-136 standard.